1. Technical Field
The present invention relates to a method for reducing the tilt of an optical unit during manufacturing of an image sensor, and more particularly, to a method for reducing the tilt of an optical unit during manufacturing of an image sensor that can improve the yield rate by carrying out a preheating process to stabilize the process environment.
2. Description of Related Art
FIG. 1A is a schematic view illustrating a structure of a conventional image sensor. FIG. 1B is a schematic view illustrating tilting and consequent fracture of a transparent plate during a process of manufacturing the conventional image sensor. FIG. 1C is a schematic view illustrating tilting of the transparent plate and consequent overflow of an adhesive during the process of manufacturing the conventional image sensor.
As shown in FIG. 1A, the conventional image sensor 100 substantially includes a circuit substrate 10 (e.g., a printed circuit board; PCB), an image sensor die 20, a transparent plate 30 and an encapsulant 40. The image sensor die 20 is disposed on the circuit substrate 10 and is electrically connected to circuits on the circuit substrate 10 via metal wirings 25 through wire bonding, and the transparent plate 30 is disposed above a photosensitive region (not shown) of the image sensor die 20 by means of an adhesive 26 such as an epoxy resin, and then the metal wirings 25 and side edges of the image sensing die 20 and the transparent plate 30 are encapsulated by the encapsulant 40 through molding.
However, as shown in FIG. 1B, if the adhesive 26 is applied uneven, and then the transparent plate 30 adhered above the photosensitive region (not shown) of the image sensing die 20 is placed in an out-of-level state (e.g., inclined in the lateral direction) during the molding process, the tilt of the transparent plate 30 with respect to the image sensor die 20 or the circuit substrate 10 will become overly large to decrease the sensing quality and this makes it easy to cause fracture of the transparent plate 30 when the mold 50 is pressed downwards during the molding process, which decreases the yield rate of image sensors.
Additionally, as shown in FIG. 1C, the air in a space enclosed by the transparent plate 30, the image sensor die 20 and the adhesive 26 during the molding process tends to expand non-uniformly when heated by a high environmental temperature. This will not only push the transparent plate 30 to cause tilting of the transparent plate 30 but also push the adhesive 26 outwards to cause overflow of the adhesive 26, thus degrading the yield rate of image sensors.